Biointerface interactions and mechanistic ecotoxicity of polystyrene micro/nanoplastics and imidacloprid in juvenile Carassius auratus under single and combined exposure.

Agricultural intensification zones-especially pesticide-intensive, ponded rice drainage belts-are overlooked hotspots for plastic and pesticide pollution. Rice-fish co-culture is now widely promoted; crucian carp is the principal co-stocked species that provides food and supports crop yield yet experiences high plastic-pesticide exposure. Imidacloprid (IMI) is among the most widely used crop pesticides and fish therapeutics, while polystyrene (PS) constitutes a major share of agricultural plastics. Juvenile carp were exposed for 28 days to PS microplastics (MP) or nanoplastics (NP) at 100μg/L, IMI at 200μg/L, and their mixtures; gills were assessed by histology, physiology, transcriptomics, and metabolomics. Exposure caused treatment-dependent gill injury. MP, NP, IMI, and NP + IMI showed positive oxidative-phosphorylation enrichment, accompanied by treatment-dependent increases in Rhesus (Rh)-family gene expression. In contrast, MP + IMI lacked this response and showed reduced Rh-family expression with the highest gill ammonia content. Weighted gene co-expression network analysis (WGCNA) identified a co-expression module associated with reduced glutathione (GSH) after false discovery rate correction, with enrichment in p53 and apoptosis-related pathways. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and transmission electron microscopy (TEM) further supported apoptosis-associated injury of pavement cells in the MP + IMI group. Integrated omics highlighted purine-related metabolite signals in MP and MP + IMI, and xanthine oxidase activity was higher in MP + IMI than in MP. Overall, this study simulated a plastic-IMI co-exposure scenario relevant to contamination hotspots in agricultural aquaculture waters and revealed pronounced branchial structural, redox-metabolic, and ammonia-homeostatic disturbances, highlighting the potential risks of plastic-pesticide mixtures in these environments.